Such flow mixers (also called "static mixers" because of the mixing elements held stationary in the tube) are often used for mixing and homogenizing substances which must be stored separately in two components but must be mixed for processing, as, for example, adhesives, sealants, paints, dental impression materials, etc. As a rule, cheap disposable mixers for a single use are involved, which are exchangeably attached to supply cartridges for the two material components (e.g. according to EP-A 0121342). Flow mixers of this kind are often used intermittently, i.e., with batchwise throughput of composition. This results in the disadvantage that the mixture tends to continue to flow or drip out of the tip of the mixer tube at the end of a "shove", this being the case especially with relatively thin media. This continued flow is, of course, a hindrance to neat working and makes exactly proportioned discharge of specific partial amounts of the mixed material impossible.
Such flow mixers can be used to advantage together with cartridges which according to an as yet unpublished proposal of the same applicant are equipped with specially designed feed pistons which can recede a little when the piston ceases to advance (Swiss Patent Application No. 00 555/87-0=EP Application No. 88101393.2, U.S. Pat. No. 4,834,268); in this connection another proposal should be mentioned (EP Application No. 0 252 401 of the same applicant; U.S. Pat. No. 4,826,053, according to which a discharge device for the operation of said cartridges is designed so that its ram driving the feed pistons forward is automatically retracted from the feed pistons immediately after each forward movement has been stopped. In any case, however, it is important that an increased internal pressure in the cartridges, as it exists during the discharge of the components, will diminish immediately and be released only towards the rear of the cartridges, i.e. toward the feed pistons or rams.